1. Field of the Invention
The present invention relates to a roll grinding system for grinding a roll used in a paper machine, and, more particularly, to a roll grinding system used to form a contoured surface on a roll for use in a paper machine.
2. Description of the Related Art
A number of different industrial processes utilize a plurality of rolls that carry a continuous sheet product. For example, a steel mill utilizes a plurality of rolls which transport the steel sheet from one end of the mill to another. A roll may be positioned adjacent to another roll and define a nip therebetween through which a metal sheet travels. A roll is typically made of steel and supported at opposite ends thereof with a bearing assembly. The length of the roll extends past the working width of the metal sheet. Because of weight considerations and the length of the roll, it is possible for the roll to sag somewhat in the middle. To achieve proper spacing between the rolls in the length direction of the roll and/or to achieve a constant nip pressure on the metal sheet across the length of the roll, it is known to provide a roll with a contoured shape to assist in maintaining a constant spacing and/or nip pressure across the length of the nip between two adjacent rolls.
A paper machine, such as a paper-making machine, typically also includes a plurality of rolls carrying wires, belts or felts (generically termed a "belt" herein), which in turn carry a fiber web from one end of the paper machine to the other end. The fiber web travels at a high rate of speed (e.g., 6000 feet/min) and it is necessary to ensure that the belts are longitudinally centered on the rolls as the fiber web moves through the machine.
One "steering" technique is to sense the lateral edge of a belt and adjust an end of the rotating roll in the paper machine during operation to shift the belt back to a longitudinally centered position. It is also known to provide a roll with a contoured shape to assist in maintaining the belt at a longitudinally centered position. For example, a roll may be formed with a crown such that the mid point along the length of the roll has a diameter which is larger than the ends of the roll.
A roll for use in a steel mill, paper machine or other application may be formed with a crown using a grinding wheel to form the contoured outer surface of the roll. A known technique is to position the grinding wheel along a travel path which is generally parallel with the longitudinal axis of the roll. By sequentially moving the grinding wheel at predefined increments along the travel path and adjusting the radial distance of the grinding face of the grinding wheel from the longitudinal axis of the roll, a crowned shape may be formed on the roll. A problem with such a technique is that a plurality of stepped shoulders are formed between adjacent grinding locations on the roll. By minimizing the travel direction in the longitudinal and radial directions between each grinding location, the stepped shoulders may be minimized but are still present. These stepped shoulders may in turn affect the quality of the manufactured sheet product.
Another known grinding technique is to utilize structure which rotates the grinding wheel about an axis which is perpendicular to the axis of rotation such that the grinding face of the grinding wheel is tangent to the area to be ground on the outer surface of the roll. Although this technique reduces the shoulders between adjacent grinds, the structure necessary to pivot the grinding wheel is relatively complex and expensive. Additionally, this technique requires that additional structure be added to the roll grinding system to allow the rotation of the grinding wheel about the pivot axis.
What is needed in the art is a roll grinding system and corresponding method of operation which allows a roll to be ground with a substantially continually smooth contoured surface, without the presence of stepped shoulders or the like.